(a) Technical Field
The present invention relates to a coolant temperature controller for a fuel cell vehicle. More particularly, the present invention relates to a coolant temperature controller for a fuel cell vehicle, in which a temperature control valve is provided at an inlet end of a fuel cell stack and the temperature control valve is proportionally controlled so that heated coolant coming from a by-pass and/or cooled coolant from a radiator is/are introduced into the stack according to a coolant temperature of the stack inlet, thus being able to provide coolant at a temperature required for optimum operation of the stack.
(b) Background Art
A fuel cell system is an electricity generation system that converts chemical energy of fuel directly into electric energy.
The fuel cell system generally comprises a fuel cell stack for generating electricity, a fuel supply system for supplying fuel (hydrogen) to the fuel cell stack, an air supply system for supplying oxygen in air, which is an oxidizing agent required for an electrochemical reaction, to the fuel cell stack, and a thermal and water management system for removing reaction heat of the fuel cell stack to the outside of the fuel cell system and controlling the operation temperature of the fuel cell stack.
The fuel cell system having the above configuration generates electricity by the electrochemical reaction of hydrogen as fuel and oxygen in air and exhausts heat and water as reaction by-products.
The fuel cell stack, which generates electricity by receiving oxygen in air and hydrogen as fuel, is used as a main power supply source of a fuel cell vehicle.
Since the fuel cell stack shows an optimal output stably when the coolant controlled at an optimal temperature is supplied to the stack, it is important to maintain the coolant introduced into the stack at a specific temperature.
Accordingly, the fuel cell vehicle includes a coolant temperature controller mounted in a fuel cell stack cooling loop to control the temperature of the coolant introduced into the stack.
FIG. 1 is a diagram showing a fuel cell stack cooling loop in a fuel cell vehicle. Upon initial start-up of a fuel cell system, when the coolant temperature is low due to a low heat generation rate of a stack 10, the coolant flows in the following order: stack 10→pump 11→temperature control valve 13→stack 10. That is, it is not necessary to send the coolant to a radiator 12 due to the low coolant temperature.
However, the heat generation rate of the stack 10 is increased with the passage of time, and thus if the temperature of the coolant flowing through the by-pass loop is rapidly increased, the temperature control valve 13 appropriately cuts off the by-pass loop and opens a radiator loop so that the coolant cooled in the radiator 12 is introduced into the stack 10 (in the following order: 10→11→12→13→10).
In view of that the coolant temperature required in the stack inlet applied to the fuel cell vehicle is about 65° C., the temperature control valve receives a signal of an inlet temperature T1 of the stack 10 to appropriately control the degree of opening of both loops so that coolant at a predetermined temperature is supplied to the stack regardless of external environment.
FIG. 2 is a diagram showing a conventional rotary type temperature control valve 130, in which a control method using a flow controller 134 by a motor mounted on the top of the valve 130 is employed.
The temperature control valve 130 comprises a first inlet port 131 through which coolant coming from a by-pass line (stack outlet) is introduced, a second inlet port 132 through which coolant from a radiator is introduced, and an exhaust port 133 through which coolant is exhausted to a stack inlet. Moreover, the flow controller 134 is provided in the valve 130 so that the coolant may be introduced through the first and second inlet ports 131 and 132 at the same time.
The above control method is a method in which the flow controller 134 provided therein is rotated left and right by the motor to control the temperature of the coolant flowing in the stack 10 by adjusting the mixing ratio of the cooled coolant coming from the radiator and the coolant from the by-pass line. With the proportional control of the flow controller 134, the control method can supply a constant amount of coolant to the stack 10.
However, the above temperature control valve 130 has a drawback in that, in the case where the rotation of the flow controller 134 by the motor is controlled under high flow conditions of more than 200 LPM, motor torque is excessively increased due to pressure generated by the coolant flow, and an accurate control thus becomes impossible. Moreover, since the rotary type temperature control valve is of high price, it is not suitable for the vehicle.
Meanwhile, FIG. 3 is a diagram showing a conventional direct-acting temperature control valve 230. The direct-acting temperature control valve 230 is operated by a motor 234 in the same manner as the rotary type valve 130. It comprises a housing including a first inlet port 231 through which coolant coming from a by-pass line is introduced, a second inlet port 232 through which coolant from a radiator is introduced, an exhaust port 233 through which coolant is exhausted to a stack inlet, and a diaphragm provided therein and selectively opening and closing the first and second inlet ports 231 and 232.
The control method associated with the direct-acting valve 230 controls a motor 234 according to the coolant temperature of the system in the same manner as that associated with the rotary type valve 130; however, there is a difference in that it alternately passes the heated coolant coming from the stack outlet and the cooled coolant from the radiator to control the coolant temperature of the system.
In this case, the diaphragm provided inside the valve housing makes the coolant coming from the stack outlet and the coolant from the radiator flow selectively by the drive of the motor.
The above direct-acting temperature control valve 230 shows a better motor control performance even under high flow conditions compared with the rotary type valve 130; however, it has a drawback in that, since it is impossible to proportionally control the cooled coolant coming from the radiator and the heated coolant from the stack, it is difficult to precisely control the coolant temperature for the stabilization of the stack output.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.